1. Field of the Invention
This invention relates to a lens barrel incorporating a motor therein and arranged to have a lens which is shiftable in the direction of the optic axis thereof driven by the rotation output of the motor.
2. Description of the Related Art
There are many known lens barrels of the kind incorporating a motor for driving a stop unit, a focusing lens or a zoom lens. The motors incorporated in the conventional lens barrels include the so-called pencil type motors (or solid type motors) such as cored motors, coreless motors and brushless motors and hollow type motors which are known from Japanese patent publication No. Sho 56-51383 and Japanese Laid-Open patent application No. Sho 56-147131. The conventional motor-incorporating lens barrel using the above-stated pencil type motor has necessitated either the provision of a protrudent part on the outside of the lens barrel for placing the motor within the lens barrel or, in order to avoid such a protrudent part, a special arrangement of the optical system of the lens barrel to increase a lens spacing interval or to stop down the light-flux passing diameter of the optical system. However, such arrangement has resulted in increases in the size and cost of the lens barrels. Further, the hollow-type motor has excessively complicated the lens barrel arrangement because of a rotor unit and stator unit which must be arranged on the inner and outer circumferential sides of lens barrel members forming the lens barrel.